1. Field of the Invention
This invention relates generally to storage access and control in multi-processor computer systems. More specifically, it relates to the updating of data in a file cache in amounts smaller than one block.
2. Background Information
Co-pending application Ser. No. 08/174,750, discloses a file cache system connected to a host computer system for improving system throughput by minimizing the Input/Output (I/O) bottleneck associated with accessing mass storage sub-systems. It achieves this goal by implementing a caching scheme on files, wherein the cached portions of files are stored in a high-speed, non-volatile storage (NVS) connected to the host system by a fiber optic interface. The unit of cached file data transferred across this interface is one block. A block consists of 28 36-bit words. However, there are occasions when the host computer system needs to update only a fraction of a block of file data in the NVS. One way of performing this operation would be to read the block containing the desired portion from the NVS back to the host system, update portions of the block with new data under software control without disturbing existing, non-referenced data, and write the updated block back to the NVS. This method is relatively slow because of the multiple dam transfers involved and the control of the update by software executing on the host system. Ideally, this merging of new data with existing data in a block should be performed by the file cache system hardware, not by software executing on the host system. This merging function could be done by novel circuitry so as to improve the throughput of the file cache system.